This invention relates generally to transparent laminates, and, more particularly, to transparent laminates having an improved ballistic response.
An example of one prior art transparent laminate of this particular type is disclosed in U.S. Pat. No. 3,700,534 to R. L. Cook. The disclosed laminate includes a glass face ply and a stretched polymethylmethacrylate substrate, with a polymethylmethacrylate cement adhesive layer disposed therebetween. Other impact resistant transparent laminates are disclosed in U.S. Pat. Nos. 4,322,476 and 4,328,277 to R. E. Molari, Jr. These two patents disclose laminates having front or impact shock receiving layers selected from the group consisting of glasses and solid resinous materials such as polycarbonate, acrylic and rubber-modified acrylics, among many other materials. The back lamina, facing away from the direction of impact, is formed of polycarbonate.
Although the transparent laminates described in these patents are generally effective in many situations, they are not believed to be entirely satisfactory. In particular, they do not have as high a ballistic response as is believed possible for a laminate of equivalent thickness and weight.
Monolithic polycarbonate and acrylic are generally not believed to be entirely satisfactory bullet-resistant materials. Laminates having several layers of these materials, however, function much better and are frequently used in bullet resistance situations.
Another monolithic material that can be used as a bullet resistant material is disclosed in U.S. Pat. No. Re. 29,772 issued to W. D. Niederhauser et al. The material is a rigid thermoplastic acrylic polymer with an elastomeric urethane impact modifier, preferably based on a polyester, an aliphatic diisocyanate and a glycol chain extender. The polymer is terminated with a vinyl-functional monomer capable of ethylenic polymerization grafting with an acrylic polymer. This material is believed to have a somewhat better impact resistance than monolithic polycarbonate, but unfortunately suffers from poor weatherability and maintains a high degree of transparency over only a relatively narrow temperature range.
It should therefore be appreciated that there still is a need for an improved transparent laminate having a high ballistic response, which can provide even higher projectile stopping power without any serious optical deficiencies. The present invention fulfills this need.